A dynamic language and bytecode vm
Switch branches/tags
Nothing to show
Clone or download
Latest commit d603e0e Nov 8, 2018



Build Status Appveyor Status

Janet is a functional and imperative programming language and bytecode interpreter. It is a modern lisp, but lists are replaced by other data structures with better utility and performance (arrays, tables, structs, tuples). The language also bridging bridging to native code written in C, meta-programming with macros, and bytecode assembly.

There is a repl for trying out the language, as well as the ability to run script files. This client program is separate from the core runtime, so janet could be embedded into other programs. Try janet in your browser at https://janet-lang.org.

Implemented in mostly standard C99, janet runs on Windows, Linux and macOS. The few features that are not standard C (dynamic library loading, compiler specific optimizations), are fairly straight forward. Janet can be easily ported to new platforms.

For syntax highlighting, there is some preliminary vim syntax highlighting in janet.vim. Generic lisp syntax highlighting should, however, provide good results.

Use Cases

Janet makes a good system scripting language, or a language to embed in other programs. Think Lua or Guile.


  • Minimal setup - one binary and you are good to go!
  • First class closures
  • Garbage collection
  • First class green threads (continuations)
  • Mutable and immutable arrays (array/tuple)
  • Mutable and immutable hashtables (table/struct)
  • Mutable and immutable strings (buffer/string)
  • Lisp Macros
  • Byte code interpreter with an assembly interface, as well as bytecode verification
  • Tailcall Optimization
  • Direct interop with C via abstract types and C functions
  • Dynamically load C libraries
  • Functional and imperative standard library
  • Lexical scoping
  • Imperative programming as well as functional
  • REPL
  • Interactive environment with detailed stack traces


API documentation and design documents can be found in the wiki. There is an introduction section in the wiki that contains a good overview of the language.


A repl is launched when the binary is invoked with no arguments. Pass the -h flag to display the usage information. Individual scripts can be run with ./janet myscript.janet

If you are looking to explore, you can print a list of all available macros, functions, and constants by entering the command (all-symbols) into the repl.

$ ./janet
Janet 0.0.0 alpha  Copyright (C) 2017-2018 Calvin Rose
janet:1:> (+ 1 2 3)
janet:2:> (print "Hello, World!")
Hello, World!
janet:3:> (os.exit)
$ ./janet -h
usage: ./janet [options] scripts...
Options are:
  -h Show this help
  -v Print the version string
  -s Use raw stdin instead of getline like functionality
  -e Execute a string of janet
  -r Enter the repl after running all scripts
  -p Keep on executing if there is a top level error (persistent)
  -- Stop handling option

Compiling and Running

Janet only uses Make and batch files to compile on Posix and windows respectively. To configure janet, edit the header file src/include/janet/janet.h before compilation.


On most platforms, use Make to build janet.

cd somewhere/my/projects/janet
make test

After building, run make install to install the janet binary and libs. Will install in /usr/local by default, see the Makefile to customize.

It's also recommended to set the JANET_PATH variable in your profile. This is where janet will look for imported libraries after the current directory.


  1. Install Visual Studio or Visual Studio Build Tools
  2. Run a Visual Studio Command Prompt (cl.exe and link.exe need to be on the PATH) and cd to the directory with janet.
  3. Run build_win to compile janet.
  4. Run build_win test to make sure everything is working.


To build janet for the web via Emscripten, make sure you have emcc installed and on your path. On a linux or macOS system, use make janet.js to build janet.js and janet.wasm - both are needed to run janet in a browser or in node. The JavaScript build is what runs the repl on the main website, but really serves mainly as a proof of concept. Janet will run much slower in a browser. Building with emscripten on windows is currently unsupported.


See the examples directory for some example janet code.

SQLite bindings

There are some sqlite3 bindings in the directory natives/sqlite3. They serve mostly as a proof of concept external c library. To use, first compile the module with Make.

make natives

Next, enter the repl and create a database and a table.

janet:1:> (import natives.sqlite3 :as sql)
janet:2:> (def db (sql.open "test.db"))
<sqlite3.connection 0x5561A138C470>
janet:3:> (sql.eval db `CREATE TABLE customers(id INTEGER PRIMARY KEY, name TEXT);`)
janet:4:> (sql.eval db `INSERT INTO customers VALUES(:id, :name);` {:name "John" :id 12345})
janet:5:> (sql.eval db `SELECT * FROM customers;`)
@[{"id" 12345 "name" "John"}]

Finally, close the database connection when done with it.

janet:6:> (sql.close db)